Photosynthesis

Photosynthesis is a biological process used by many cellular organisms to convert light energy into chemical energy, which is stored in organic compounds that can later be metabolized through cellular respiration to fuel the organism's activities.

1. Photosynthesis Importance in Bio Productivity Photochemical Process, Photochemical Reactions Vikas Kumar M.Sc (G&PB) Chaudhary Charan Singh University

2. 2 ← Table of contents Introduction Definition of Photosynthesis Steps of Photosynthesis Site of Photosynthesis Chloroplast as Solar Harvesting Unit Pigments and Its types in Plants Mechanism of Photosynthesis Light Reaction (Photosystems, Cyclic and Non Cyclic Phosphorylation) Dark Reaction Importance in Bio-productivity References

3. 3 Introduction Photosynthesis by far the most significant biological process on the planet earth. It is through this phenomenon that all the useful organic matter is available on the earth has been produced. The leaves in the higher plants may be regarded as machinery engineered to undertake photosynthesis efficiently even under very hostile environments. Photosynthesis is not a monopoly of green plants but is also occurs in cyanobacteria and photosynthetic bacteria.

4. 4 W hat is Photosynthesis? “ Photosynthesis can be defined as the anabolic process during which complex energy rich organic molecules/ compounds are synthesized by organisms from CO2 and H2O using solar energy.” In higher and other non-flowering plants the photosynthetic reactions occur in the chloroplast – “An Incredible Thermodynamic Machine.”

5. 5 Steps of Photosynthesis : During photosynthesis, light energy from the sun is absorbed by chlorophyll. Water from the soil is absorbed by the root hairs and is transported to the leaves. Carbon dioxide from the air enters through the stomata of the leaves. In the meantime, water molecules are split into hydrogen and oxygen. This hydrogen and carbon dioxide then combine to form carbohydrates (glucose). Glucose is the source of energy that provides growth and development. Later, it is converted into starch and is stored in different plant organs.

6. 6 Site of Photosynthesis Photosynthesis occurs in chloroplasts of the plants cell. All green parts of plants are having chloroplasts and carry out photosynthesis. Majorly chloroplasts are found in leaves. The green color comes from the chlorophyll in the chloroplasts. The pigments absorbs light energy according to their absorption capacity. Chlorophyll is the green pigment which captures light for photosynthesis.

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8. 8 C hloroplast : A Solar Harvesting Unit Chloroplast was first described by a German Botanist Von Mohl in 1837. A single leaf cell may contain as many as 50 chloroplast, each with a 4-6 µm diameter and surrounded by a double membrane. The inner membranes of chloroplast are folded into sacs or vesicles known as thylakoids and often many thylakoids are stacked one above the other, in flattened columns to form Granum.

9. 9 C hloroplast : A Solar Harvesting Unit Surrounding the thylakoid membrane system is a semi fluid substance called “Stroma.” Within the thylakoid membranes, photosynthetic pigments are organized n a network called the “Photosystem” capable of capturing photons of light. The photosystem functions a huge antenna, amplifying the power of individual pigment molecules to capture light.

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12. 12 A plant pigment is any type of colored substance produced by a plant. These colouring substance are also called Biological Pigments or Biochromes. P lant pigments are following types:- Chloro phyll : Primary pigment found within the plants cells of all green plants. Most significant and essential for photosynthesis. Chlorophyll is f urther classified in following: Chlorophyll a – Found in algae, cyanobacteria & all higher plants. Chlorophyll b – Found only in Green algae and in higher plants. Chlorophyll c – Found in some marine algae. Chlorophyll d – Found only in Red algae Chlorophyll e – Found only in algae. Among all these pigments, Chl. a and Chl. b are considered as the primary photosynthetic pigments. Pigments and their types in plants:

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14. 14 2. Carotene: Carotenoids are the pigments in the form of orange, red and yellow colours . Insoluble in water and attached to the membranes of the cell bodies. 3. Anthocyanins: A type of flavonoid pigment naturally found in all the tissues of higher plants. This pigment provide colour mainly to fruits and flowers. 4. Flavonoids: Yellow coloured pigments found in lemons and oranges. Largely found in the plastids and cytoplasm of the plant cell. Pigments and their types in plants:

15. 15 Photosynthesis comprises two phases: The first phase is the photochemical phase or  light-dependent process . This phase is commonly known as the light reaction . The second phase is the biosynthetic phase of the dark reaction of photosynthesis. This phase is the  light-independent process. The whole process of photosynthesis takes place within the chloroplast. Mechanism of Photosynthesis:

16. 16 1. Light Reaction The light reaction is a light-dependent process which includes a series of events such as light absorption, hydrolysis, the release of oxygen, formation of ATP and NADPH. The light reaction of  photosynthesis   initiates only when it is supplied with light energy. The photosystem is the arrangement of pigments, including chlorophyll within thylakoids. There are two photosystems in plants: a. Photosystem I (PS-I) b. Photosystem II (PS-II) Mechanism of Photosynthesis: 1. Light Reaction The light reaction is a light-dependent process which includes a series of events such as light absorption, hydrolysis, the release of oxygen, formation of ATP and NADPH. The light reaction of  photosynthesis   initiates only when it is supplied with light energy. The photosystem is the arrangement of pigments, including chlorophyll within thylakoids. There are two photosystems in plants: a. Photosystem I (PS-I) b. Photosystem II (PS-II) Mechanism of Photosynthesis:

17. 17 The light reaction occurs in the thylakoids of the chloroplast. When the light hits, chlorophyll- a  gets excited to a higher energy state followed by a series of reactions. This energy is converted into energy molecules ATP and NADPH by using PS I and PS II.  Also, hydrolysis occurs and releases oxygen. Mechanism of Photosynthesis:

18. 18 Photosystems are the functional units for photosynthesis, defined by a particular pigment organization and association patterns, whose work is the absorption and transfer of light energy, which implies transfer of electrons. Physically, photosystems are found in the  thylakoid  membranes. There are two kinds of photosystems:  photosystem I  (PSI) and  photosystem II  (PSII).  PSII  acts first during the light transformation process in photosynthesis, but it was named PSII because it was discovered second. Photosystems :

19. 19 Each photosystem consists of two closely linked components: the first is the antenna complex formed by hundreds of pigment molecules that capture photons and transfer the harvested light energy to the second component named the reaction center, which possesses Chl a molecules in a matrix of protein. When excitation energy reaches chlorophyll a at the reaction center, electron transfer is initiated through an  electron transport chain . PSI  is located at the outer surface of the thylakoid membrane, and contains chlorophyll b; chlorophyll a and  carotenoids. PSII is located at the inner surface of the thylakoid membrane, and contains chlorophyll b; chlorophyll a, phycobillins and xanthophylls.

20. 20 Photosystems are the functional and structural elements of photosynthetic protein complexes. They work together to carry out light absorption, energy and electron transport. Components of photosystem: Antenna Complex:  light-harvesting complex made up of proteins and numerous pigments. Reaction centers:  M olecules of chl. A & principal electron acceptor.

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22. 22 Photophosphorylation “ Formation of ATP form ADP and iP (Inorganic Phosphate) in the presence of light.” Cyclic Photophosphorylation Performed by PS I independently. External source of electrons is not required. Same electrons are recycled. Synthesizes only ATP. Operates under low light intensity. Occurs in stromal thylakoid.

23. 23 Non-Cyclic Photophosphorylation Performed by PS I and PS II. Electrons are supplied by photolysis of water. Synthesizes ATP and NADPH. Operates under optimum light. Occurs in granal thylakoids

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25. 25 2. Dark Reaction Dark reaction is also called carbon-fixing reaction. It is a light-independent process in which sugar molecules are formed from the carbon dioxide and water molecules. The dark reaction occurs in the stroma of the chloroplast, where they utilize the products of the light reaction. Plants capture the carbon dioxide from the atmosphere through stomata and proceed to the  Calvin cycle . In the Calvin cycle, the ATP and NADPH formed during light reaction drives the reaction and convert six molecules of carbon dioxide into one sugar molecule, i.e. glucose. Mechanism of Photosynthesis:

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27. 27 Role of Photosynthesis in Bio-productivity : Photosynthesis is a crucial process for the productivity of the biosphere. It is the primary mechanism through which energy from the sun is captured and converted into organic compounds that sustain life. Photosynthesis occurs in green plants, algae, and some bacteria, and it is responsible for producing the vast majority of the oxygen in the Earth's atmosphere. The importance of photosynthesis in bio productivity can be understood through the following points: Energy Source: Photosynthesis is the primary source of energy for most living organisms on the planet. Plants, algae, and some bacteria use photosynthesis to produce organic compounds that are consumed by other organisms, including animals and humans.

28. 28 2. Oxygen Production: Photosynthesis also plays a critical role in producing the oxygen that all living organisms require for respiration. Without photosynthesis, the levels of oxygen in the atmosphere would be significantly lower, making it difficult for most organisms to survive. 3. Carbon Fixation: Through photosynthesis, plants and algae capture carbon dioxide from the atmosphere and use it to build organic molecules. This process is known as carbon fixation and is essential for reducing the amount of carbon dioxide in the atmosphere, which is a greenhouse gas that contributes to climate change.

29. 29 4. Food Production: Photosynthesis is the foundation of most food chains and is the basis for the production of crops and other food sources. The carbohydrates, proteins, and fats produced by plants through photosynthesis serve as the primary source of nutrients for animals and humans. In summary, photosynthesis is essential for maintaining the productivity of the biosphere. It provides the energy and organic compounds necessary for most living organisms to survive, produces oxygen for respiration, fixes carbon dioxide, and forms the basis of food chains and agriculture.

30. 30 References Plant Physiology: Theory and Applications, SL Kochar and Sukhbir Kaur Gujral (Book) Matthew P. Johnson, Photosynthesis (article) Encyclopedia.com Sciencedirect.com Biologyonline.com Byjus.com Picture are taken from various internet sources.

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